Field of the Invention
The present invention relates to a printing apparatus which prints an image on a printing medium by discharging an ink droplet from each ink orifice arranged in a printhead, and a method for exhausting bubbles from the ink channel of the printing apparatus.
Description of the Related Art
A printing apparatus which prints by discharging ink from the orifices of a printhead to a printing medium includes an ink channel for supplying ink to ink droplet orifices from an ink tank storing the ink. If a bubble which moves by the flow of ink at the time of printing exists in the ink channel, the bubble reaches the orifice, hinders discharge of ink, and causes a print failure. To prevent such a print failure, various techniques have been proposed.
For example, Japanese Patent Laid-Open No. 2007-98959 has disclosed an arrangement in which a valve is arranged in an ink channel between an ink tank and an orifice, and opening/closing of the valve is controlled to increase a suction negative pressure and increase the fluid velocity in the ink channel, thereby improving the bubble exhaust performance from the ink channel. Japanese Patent Laid-Open No. 2004-58398 has disclosed an arrangement in which the bubble exhaust performance from the ink channel is improved by alternately repeating opening/closing of a valve.
Further, Japanese Patent Laid-Open No. 6-55742 has disclosed the following arrangement in order to efficiently exhaust a bubble mixed in an ink orifice and ink chamber. More specifically, an ink supply port, bubble supply port, and bubble suction port are arranged in the ink chamber. A bubble is supplied from the bubble suction port into the ink chamber, and a bubble coalescent with tiny bubbles generated in the ink orifice and ink chamber is exhausted from the bubble suction port.
However, if the suction negative pressure is increased to increase the fluid velocity in the ink channel by using the bubble exhaust arrangements disclosed in Japanese Patent Laid-Open Nos. 2007-98959 and 2004-58398, even the ink fluid flow is also increased. As a result, a large amount of ink is wastefully consumed owing to the high fluid flow. Japanese Patent Laid-Open No. 6-55742 does not describe handling of a bubble generated in the ink channel for supplying ink to the printhead from the ink tank storing the ink.